The technical problem is that of precisely mounting a component hereinafter called a “bridge” on a structure, hereinafter called a “plate”. Precision assembly must be performed with a high level of positioning precision on the one hand and alignment precision on the other hand, generally obtained using centring pins and reference bores that cooperate with each other. Unless the bridge and plate are made simultaneously on the same fabricating means, it is difficult to obtain positioning via the cooperation between two centring pins and the corresponding bores. If the components are made separately, close tolerances must be assigned to the fabrication in order to respect the distances between two centring elements. The different thermal expansion and, more generally, deformation behaviour of the components that are assembled to each other does not facilitate high quality assemblies.
In practice, a male centring means, such as a centring pin, cooperates with a female centring means, such as a centring bore, or vice versa, and the centring thereby achieved defines a theoretical pivot axis about which the bridge can pivot relative to the corresponding plate. To ensure precision assembly, it is important to able to angularly position the bridge perfectly relative to the plate. Thus the plate generally includes a female alignment means, preferably a linear guide, which cooperates with a male guide means, generally formed by a pin, comprised in the bridge, or vice versa. Naturally there must be some radial play relative to the pivot and in the direction of linear guiding in order to compensate for the relative deformations of the bridge relative to the plate, and especially any displacement between the bridge and the plate.
The centring means on the bridge side is generally formed by a milled pivot, a pin or a screw foot, of cylindrical shape, cooperating with a bore in the plate.
The alignment means on the bridge side is also formed by a milled pivot, a pin or a screw foot, of cylindrical shape, cooperating with a hole or elongated groove in the plate.
To ensure assembly and especially removal, there is generally some play between the male centring means and the female centring means. This play compromises the positioning precision and the rigidity with which the bridge is held, in the assembly line.
However, it is known to provide a force-fit for the alignment means, so that, for example, a groove in the plate only cooperates with two short segments of the periphery of a pin fixed to the bridge. Thus, the bridge always remains removable, and a high level of alignment can be ensured because of the force-fit.
It will be noted that it is also known to perform centring with an elastic, slit, cylindrical pin, which cooperates with a cylindrical bore. However concentricity between the free state and compressed state of the pin is not guaranteed, nor is the gripping value achieved.
Assemblies with triangular pins cooperating with a smooth bore, such as those disclosed in DE Patent No. 2 034 993 in the name of Precision Industries are also known.
CH Patent No 669 680 A2 in the name of Richemont Int. S.A. discloses a device for securing a mobile component, fabricated in a fragile material, onto a support element, in particular for positioning between a bridge and a plate. This mobile component has an aperture for receiving the support element, and it includes an elastically deformable intermediate part, fixed in the aperture and including a central hole. The intermediate part redistributes part of the stresses exerted by the support element when the latter is driven into the central hole. The aperture may have faces in a polygonal cross-section, cooperating with a cylindrical pin forming the support element.
FR Patent No 2, 282 553 in the name of ETA S.A. discloses the positioning of an element on a frame using three stop members with which the element cooperates via three surfaces thereof.